Embodiments of the invention are directed to the field of optofluidics, particularly, to optofluidic apparatus, methods, and applications and, more particularly, to reconfigurable optofluidic apparatus, methods, and applications.
Reconfigurable systems are those in which some or all of a system's physical, chemical or electrical properties can be changed, either on-command to enhance functionality or autonomously in response to a change in external/internal conditions. Such systems are ubiquitous in nature and have recently been realized in a wide range of engineering applications including self-healing polymers, self-reproducing and dynamically reconfigurable robots, morphing aircraft, computing, and adaptive space structures. In electronics, the ubiquitous reconfigurable system is the Field Programmable Gate Array (FPGA), which is a semiconductor device that can be reprogrammed by the user at any time post-fabrication to perform any arbitrary set of logical functions. Such devices have brought a number of benefits particularly to military systems including, but not limited to, reduced cost (e.g., where relatively few pieces are required it is much cheaper to purchase and program off-the-shelf FPGAs than design an application specific integrated circuit) and increased security (e.g., FPGAs can be designed to self-erase the programmed circuitry making it difficult to reverse engineer captured devices). Despite the advantages demonstrated in the electronics' field and the importance of photonic systems to current and emerging applications, at present there is not an equivalently ubiquitous FPGA-type technology for photonics.
A recognized key requirement for reconfigurable optical systems is the ability to dynamically control either (1) the physical layout or (2) the refractive indices of the optical components. Recent advancements in optical MEMS technology have enhanced functionality and flexibility with regards to (1) but are fundamentally limited in the degree to which the systems can be manipulated (achievable physical displacements in MEMS are small and must be predefined) and greatly increase device fabrication complexity. With regards to (2), traditional techniques for manipulating the refractive index through the application of electric, acoustic, thermal, and mechanical strain fields are limited by the achievable Δn/n (i.e., the achievable change in refractive index divided by the base refractive index). Optofluidic technology has the potential to offer an order of magnitude jump in this quantity over these existing approaches.
In addition to enabling rapid reconfigurability, optofluidic-based photonics technology may provide inherent advantages in terms of temperature stabilization due to the incorporation of liquids into the optical structure. In general the heat transfer coefficient (which is the proportionality constant between heat rejection and surface temperature) for systems immersed in air ranges from 10 W/m2K to 100 W/m2K, whereas for liquids they are closer to 500 W/m2K to 10,000 W/m2K. As such, it may be possible to decrease a device's temperature rise for a given heat rejection requirement by an order of magnitude (such that a 10° C. increase in temperature for a traditional device would result in a 1° C. increase in an optofluidic device. It has also recently been demonstrated that incorporation of liquids into a device structure can automatically compensate for thermo-optic effects. In addition, similar fluid based opto-electronic systems have demonstrated increased radiation resistance and, optical data storage densities as high as 33× that of the current Blu-ray standard.
Microfluidics can be defined as the study or use of the motion of fluids in confined systems where the fundamental length scale is between 100 nanometers (nm) and 1 millimeter (mm). In this context, modern microfluidics can be traced back to the development of a silicon chip-based gas chromatograph at Stanford University and the inkjet printer at IBM. However, the concept of the integrated microfluidic device as it is known today was not proposed until the early 1990s by Manz et al. Since that time the field has developed to a point where fluid flow and species transport on these scales can be accomplished by a number of elegant techniques, a few of which include: pressure driven flow, electrokinetics, buoyancy, magnetohydrodynamics, capillarity, electrowetting, and thermocapillarity.
It was earlier thought that the bioanalytical improvements associated with the scaling down of the size of these devices (which came to be known as labs-on-a-chip) would be the biggest advantage of these devices. Further developments however revealed other significant advantages including: minimized consumption of reagents, increased automation, thermal stabilization and reduced manufacturing costs. As a result of these advantages, the field has blossomed into many different areas ranging from biological and chemical analysis, point-of-care testing, clinical and forensic analysis, and molecular diagnostics. As embodied herein below, the advantages of microfluidics in terms of being able to shuttle chemicals around on a chip will be translated to shuttling light around.
The origin of the macroscopic liquid optical devices can be traced as far back as the 18th century. More recent advancement in microfluidic technology have enabled the development of present day equivalents of such devices centered on the marriage of microfluidics and optics. Since 2005, these efforts have matured into a new research field known as “optofluidics.” Some of the more prominent examples of such devices include: liquid crystal infused photonic crystal lasers, fluid-fluid waveguides, florescent light sources, polarization independent fluidic switches, microfluidically tuned optical fiber and interferometers, electronic paper, high resolution in-chip lensless microscopy, and a variety of biomolecular sensor platforms and optical manipulation techniques.
Early on, reconfigurable photonics was viewed as one of the major applications of optofluidic technology. This led initially to the development of adaptable fluid optical lensing technologies using electrowetting based approaches. Later versions of these devices included planar lenses more practical for on-chip integration, reconfigurable waveguiding approaches, designs that enable focusing in three dimensions, and self-assembled minors using Janus particles. The advantage of these devices in the context of reconfigurable photonics vs. solid lenses was in their ability to simultaneously change the physical shape and refractive index profile of the lens (i.e., one could build a system that would allow for automatic refocusing and aberration correction).
In 2006, the first example of the use of nanofluidics to create reconfigurable silicon photonic crystals was reported. Traditionally refractive index modulation in silicon is limited to the exploitation of relatively weak non-linear material properties. As a result, devices require either long interaction lengths, high operational power, or the incorporation of resonant elements to enhance the effect. The use of these elements leads either to very large devices or low bandwidth. Two other limitations include long switching times and extension to greater degrees of adaptability. Since these systems required transport through a nanochannel, the hydrodynamics were such that only very low flow rates could be obtained, resulting in switching times on the order of 20 s. Moreover, the elements of a silicon photonic crystal must be extremely close packed (on the order of 350 nm periodicity) in order to maintain a full bandgap. As such, the development of a mechanical valving infrastructure to enable arbitrary flow routing poses an extreme fabrication and integration challenge.
The inventors have thus recognized advantageous and beneficial solutions to the aforementioned disadvantages and problems in the prior art via reconfigurable optofluidic apparatus and methods according to embodiments of the invention disclosed below.